The present invention relates to a method for processing manure, fermented manure or waste water having a relatively high ammonium nitrogen concentration, said liquid manure being subjected to nitrification in a first step and to denitrification in a subsequent step, an aerated reactor which contains active sludge rich in nitrifying bacteria being used in the nitrification step and acid-neutralizing chemicals being added to said reactor if necessary and a continuously fed upflow slib bed (USB) reactor which contains a very compact biomass which is capable of converting nitrate to nitrogen gas and to which an organic substrate is added for use in the denitrification step.
A method of this type is known from, inter alia, Agrarisch Dagblad of Mar. 14, 1988. With this method the liquid fraction of fermented semi-liquid manure is treated. The biologically degradable organic substances, nitrifiable nitrogen and phosphorus which are present in the liquid fraction of anaerobic or fermented semi-liquid manure can be largely removed. The method essentially consists in a coupling of a nitrification step in a nitrification reactor in which ammonia is converted by bacteria to oxidized nitrogen with a denitrification step in a denitrification reactor in which oxidized nitrogen is converted by bacteria to nitrogen gas, the phosphate present in the liquid being concentrated as a chemical precipitate in the reactor at the same time. Oxidation of ammonia results in lowering of the pH, which, with this method, can be countered by metering in lime and/or metering in effluent from the denitrification reactor (recycling) to the nitrification reactor. During the nitrification step of this method there will also be some removal of nitrogen and phosphate since the bacteria degrade biologically degradable substances which have passed through the fermentation to give CO.sub.2 and H.sub.2 O. The nitrogen and phosphorus thus liberated can be incorporated in the new cells of the active sludge. With this method the nitrification reactor (which can be either a fed batch reactor or a batch reactor) is operated batchwise. It is then aerated until all ammonia has been nitrified, after which the aeration is stopped temporarily in order to allow the sludge to settle. The nitrified liquid manure is run off for treatment in the denitrification step, while the active sludge remains behind in the nitrification reactor for a subsequent cycle. In the denitrification step the effluent from the nitrification reactor is pumped upwards through a USB (upflow slib bed) reactor. In this reactor there is a very compact biomass which is capable of converting nitrate to nitrogen gas. In order to allow this step to proceed, an organic substrate--for example methanol--must be added to the reactor. Acid is consumed during the denitrification step, as a result of which the pH in the bacterial bed rises. As a consequence of this rise, an insoluble precipitate of phosphate with the calcium ions present in the liquid forms. The manure processing consisting of manure fermentation and separation of fermented manure, followed by the method for treatment of the liquid fraction of fermented semi-liquid manure, which has been described above, and is shown in FIG. 1.
A number of manure processing works are being developed at present, for example Promest in Helmond and Memon in Deventer. In these works semi-liquid manure is evaporated to give a dry product, which costs a great deal of energy since semi-liquid manure consists to more than 90% of water. Moreover, this evaporation is a complex technology which in fact still has to be developed for use on manure. The cost price of processing of this type for the formation of dry granular or powder manure is consequently very high.
An approach which differs from that described above is the treatment of semi-liquid manure in conventional effluent treatment installations. Currently this is also being used for treatment of liquid manure from calves. The conventional manure treatment has the significant disadvantages that the process produces a large amount of sludge (excess bacteria) and that the process is not capable of removing the phosphate. This means that extra provisions have to be made for sludge treatment and dephosphating. A conventional manure treatment also requires a fairly large amount of space.
This method, as reported in Agrarisch Dagblad of Mar. 17, 1988, has the advantage that it is relatively inexpensive and can be carried out in a compact installation. However, a number of problems also arise in this case in the treatment of fermented manure.
A compact manure treatment installation for manure and fermented manure or ammonium nitrogen containing waste water can be produced and maintained only if:
a) the metering of the fermented liquid fraction is matched to the nitrification capacity of the nitrification reactor. The nitrification reactor must not be overloaded but must also not operate underloaded. PA0 b) The metering of methanol (or other sources of carbon) to the denitrification reactor is matched to the nitrate load in the denitrification reactor. In the case of undermetering, however, methanol (or other source of carbon) is present in the effluent to be discharged. PA0 c) The effluent recycling from denitrification reactor to nitrification reactor is controlled such that it is optimum. Too little recycling leads to a nitrate concentration which has an inhibitory action on the bacteria; too much recycling has the consequence that the reactor is filled mainly with liquid which has already been treated. PA0 the incoming nitrogen load; PA0 the information from the WAZU respiration meter (Netherlands Patent Application No. 8600396, filed on Feb. 17, 1986); PA0 the pH in the nitrification reactor, the criterion for which is that it is in the range limited by 6 and 8.5; PA0 the temperature in both the nitrification reactor and the denitrification reactor, the criterion for which is that this is lower than 40.degree. C.; PA0 the concentration of oxidized nitrogen in the influent for the denitrification reactor, the criterion for which is that the concentration is between 0 and 4 g N/1; PA0 the concentration of oxidized nitrogen in the nitrification reactor, the criterion for which in the sludge/liquid mixture in the reactor is that the concentration is between 0 and 4 g N/1; PA0 the concentration of the carbon source in the effluent from the denitrification reactor; PA0 the gas production in the denitrification reactor.
Said points can be achieved by the use of separate instruments, it being necessary to carry out some of the diverse operations by hand. Moreover, the results of the various measurements cannot be integrated and translated into a control action without the intervention of one operator. Furthermore, the effluent from the nitrification reactor can still contain organic substances which cannot be further degraded in the nitrification reactor. Organic material which passes into the denitrification reactor can be converted into inorganic material in that reactor with the liberation of ammonium nitrogen which is then (insofar as it is not fed via the recycle stream) discharged with the effluent.